Chain straightening

McMillan, F.M. (1979) The Chain Straighteners - Fruitful Innovation the Discovery of Linear and Stereoregular Synthetic Polymers (Macmillan, London). 

Frank M. McMillan. The Chain Straighteners. New York Macmillan, 1979. 

McMillan, F. M. The Chain Straighteners Fruitful Innovation. The Discovery of Linear and Stereoregular Polymers. 1981, The Macmillan Press Ltd. London, U.K. 

B is correct. Isoprene is a diene (alkene), which occupies an irregular shape as a result of all those double bonds. When stretched, disorganized chains straighten out but can always revert back to their original random state. Isoprene vulcanization (cross-link induction) serves to prevent stretching. 

The chain retains its zigzag shape except at the double bond site and triple bond site, where the chain straightens out. To form these bonds, carbon electrons must be stretched into new locations. 

McMillan, E M. 1979. The chain straighteners. Fruitful innovation The discovery of linear and stereoregular synthetic polymers. London Macmillan Press. Morawetz, M. 1985. Polymers The origins and growth of a science. New York, NY "Wiley Intersdence. 

Due to their narrow aperture, zirconocene-based catalysts insert olefins almost exclusively in the 1,2- or primary direction. Small proportions of 2,1-inserted propylene units and, for some catalysts, 1,3-inserted units derived from them by chain straightening, are a cause of melting-point lowering in some metallocene-produced polypropylenes. 

Discussion Point DPS The previously unexpected observation of side-chain branches in diimine-nickel catalyzed polyethylene formation is explained by the reaction scheme represented in Figure 15. Propose related chain migration schemes which explain i) the chain straightening , i.e. the incorporation of propylene methyl substituents into the backbone of polypropylene chains produced by these catalysts, ii) the 2,co-concatenation of higher a-olefins by some Ni-based catalysts, and Hi) the introduction of stereoerrors in isotactic polypropylene by chain-migration of chiral ansa-zirconocene catalysts. 

FM McMillan, The Chain Straighteners, MacMillan Publishing Company, London (1979). DM Kiefer, Today s Chemist at Work, June 1997, p 51. 

F. M. McMillan The Chain Straighteners, The McMillan Press, London, 1979. 

Organometallic mixed catalysts for ethylene polymerization, discovered (by serendipity) when nickel-contaminated autoclaves were used to carry out an Aufhaureaktion (reaction of A1(C2H5)3 with ethylene). The nickel effect lead to the zirconium-catalyzed ethylene polymerization in Ziegler s laboratory on October 26, 1953, see F. M. MacMillan, The Chain Straighteners, The MacMillan Press Ltd., p. 62f., London, 1979. 

The second step of adsorption is much slower and is zeroth order with respect to the thiol concentration20. Saturation is usually reached after 16-24 h of exposure. During this step, the monolayer reorganizes, producing well-packed structure and freeing some more gold surface which is immediately occupied by additional thiol molecules. The alkane chains straighten and the order and orientation of the monolayer... 

The rigidity of rubber is increased by cross-linking the polymer chains with disulfide bonds. When rubber is stretched, the randomly coiled chains straighten out and orient themselves along the direction of the stretch. 

The living nature of the nickel-catalyzed a-olefin polymerizations coupled with the propensity for chain straightening of longer a-olefins can be utilized to prepare block copolymers with well-defined architectures. For example, the synthesis of a-olefin A—B—A block copolymers where the semicrystalline A blocks are made up of poly(l-octadecene) and the B block is composed of a more highly branched, amorphous, random copolymer of propylene and 1-octadecene enabled the preparation of thermoplastic elastomeric polyolefins. ... 

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